Although Rob Braun's handy CDEV "SetDate" worked fine on my Mac SE/30 using System 6 or 7, it froze on my Powerbook 1400c using OS 8.0
This article comes to the rescue on how to use ResEdit to fix the problem on all Macs from the Mac 512 up through those running OS 8.x.
Apple fixed the problem in OS 9: